chore: fix flaky test + remove unused code (#6486)

Description
---
Fix flaky test `test_listening_initial_fallen_behind`
Removed unused code

Motivation and Context
---
We should not have unused code the code base.

How Has This Been Tested?
---
unit tests

base_layer/core/src/proof_of_work/difficulty.rs

@@ -113,25 +113,6 @@ impl Default for Difficulty {
     }
 }
 
-/// This trait is used to add a type to `CheckedAdd`, which greatly simplifies usage in the code.
-/// It is implemented for `Difficulty` and `u64`.
-pub trait CheckedAdd<T> {
-    fn checked_add(&self, other: T) -> Option<Self>
-    where Self: Sized;
-}
-
-impl CheckedAdd<Difficulty> for Difficulty {
-    fn checked_add(&self, other: Difficulty) -> Option<Self> {
-        self.0.checked_add(other.0).map(Difficulty)
-    }
-}
-
-impl CheckedAdd<u64> for Difficulty {
-    fn checked_add(&self, other: u64) -> Option<Self> {
-        self.checked_add(Difficulty(other))
-    }
-}
-
 impl From<Difficulty> for u64 {
     fn from(value: Difficulty) -> Self {
         value.0
@@ -164,25 +145,7 @@ pub trait DifficultyAdjustment {
 mod test {
     use primitive_types::U256;
 
-    use crate::proof_of_work::{
-        difficulty::{CheckedAdd, MIN_DIFFICULTY},
-        Difficulty,
-    };
-    #[test]
-    fn add_difficulty() {
-        assert_eq!(
-            Difficulty::from_u64(1_000).unwrap().checked_add(8_000).unwrap(),
-            Difficulty::from_u64(9_000).unwrap()
-        );
-        assert_eq!(
-            Difficulty::default().checked_add(42).unwrap(),
-            Difficulty::from_u64(MIN_DIFFICULTY + 42).unwrap()
-        );
-        assert_eq!(
-            Difficulty::from_u64(15).unwrap().checked_add(5).unwrap(),
-            Difficulty::from_u64(20).unwrap()
-        );
-    }
+    use crate::proof_of_work::{difficulty::MIN_DIFFICULTY, Difficulty};
 
     #[test]
     fn test_format() {
@@ -203,14 +166,6 @@ mod test {
         assert_eq!(Difficulty::max().as_u64(), u64::MAX);
     }
 
-    #[test]
-    fn addition_does_not_overflow() {
-        let d1 = Difficulty::from_u64(100).unwrap();
-        assert!(d1.checked_add(1).is_some());
-        let d2 = Difficulty::max();
-        assert!(d2.checked_add(1).is_none());
-    }
-
     #[test]
     fn be_high_target() {
         let target: &[u8] = &[

base_layer/core/src/test_helpers/mod.rs

@@ -43,7 +43,7 @@ use tari_utilities::epoch_time::EpochTime;
 use crate::{
     blocks::{Block, BlockHeader, BlockHeaderAccumulatedData, ChainHeader},
     consensus::{ConsensusConstants, ConsensusManager},
-    proof_of_work::{difficulty::CheckedAdd, sha3x_difficulty, AchievedTargetDifficulty, Difficulty},
+    proof_of_work::{sha3x_difficulty, AchievedTargetDifficulty, Difficulty},
     transactions::{
         generate_coinbase_with_wallet_output,
         key_manager::{MemoryDbKeyManager, TariKeyId},
@@ -185,8 +185,8 @@ pub fn create_peer_manager<P: AsRef<Path>>(data_path: P) -> Arc<PeerManager> {
 pub fn create_chain_header(header: BlockHeader, prev_accum: &BlockHeaderAccumulatedData) -> ChainHeader {
     let achieved_target_diff = AchievedTargetDifficulty::try_construct(
         header.pow_algo(),
-        Difficulty::min().checked_add(1).unwrap(),
-        Difficulty::min().checked_add(1).unwrap(),
+        Difficulty::from_u64(Difficulty::min().as_u64() + 1).unwrap(),
+        Difficulty::from_u64(Difficulty::min().as_u64() + 1).unwrap(),
     )
     .unwrap();
     let accumulated_data = BlockHeaderAccumulatedData::builder(prev_accum)

base_layer/core/tests/tests/node_state_machine.rs

@@ -53,6 +53,7 @@ use tokio::{
     sync::{broadcast, watch},
     task,
     time,
+    time::sleep,
 };
 
 use crate::helpers::{
@@ -233,6 +234,8 @@ async fn test_listening_initial_fallen_behind() {
 
     let (state_change_event_publisher, _) = broadcast::channel(10);
     let (status_event_sender, _status_event_receiver) = watch::channel(StatusInfo::new());
+    // This is here so that we can let the initial states run through the channels
+    sleep(Duration::from_secs(1)).await;
     let mut alice_state_machine = BaseNodeStateMachine::new(
         alice_node.blockchain_db.clone().into(),
         alice_node.local_nci.clone(),